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Period change and stellar evolution of $β$ Cephei stars

The $β$ Cephei stars represent an important class of massive star pulsators probing the evolution of B-type stars and the transition from main sequence to hydrogen-shell burning evolution. By understanding $β$ Cep stars, we gain insights into the detailed physics of massive star evolution such as rotational mixing, convective core overshooting, magnetic fields and stellar winds, all of which play important roles. Similarly, modeling their pulsation provides additional information into their interior structures. Furthermore, measurements of the rate of change of pulsation period offer a direct measure of $β$ Cephei stellar evolution. In this work, we compute state-of-the-art stellar evolution models assuming different amounts of initial rotation and convective core overshoot and measure theoretical rates of period change for which we compare to rates previously measured for a sample of $β$ Cephei stars. The results of this comparison are mixed. For three stars, the rates are too small to infer any information from stellar evolution models, whereas for three other stars the rates are too large. We infer stellar parameters, such as mass and age, for two $β$ Cephei stars: $ξ^1$ CMa and $δ$ Cet, that agree well with independent measurements. We explore ideas for why models may not predict the larger rates of period change. In particular, period drifts in $β$ Cep stars can artificially lead to overestimated rates of secular period change.